Canada geese (Branta canadensis) nesting on elevated structures in urban Indiana, USA

Abstract The Canada goose (Branta canadensis) population has radically changed over the past 60 years—from once being extirpated in the state of Indiana to the current level of approximately 113,000. High urban densities have resulted in persistent human–wildlife conflicts and novel interactions between geese and their physical environment. Canada geese typically choose nest sites that are on the ground or slightly elevated sites such as muskrat lodge, but we report observations of Canada geese nesting on rooftops 2.6–12.2 m above ground level in central Indiana. These observations suggest that alternative, unpredicted nesting sites are being chosen over more traditional sites, in a likely attempt to reduce risks of disturbance and predation. This atypical nest‐site selection may pose new management challenges, but further research is needed.

Prior to the extensive recovery of Canada goose populations, wildlife managers used culverts and raised platforms to aid in nesting and recruitment (Mackey et al., 1988). These artificial nest structures were predicated on a well-documented understanding that elevated nesting (e.g., raised platforms) minimizes nest predation risk (Anderson et al., 2015).
This phenomenon is observed in natural nesting behaviors as well. In the goose family, several species have been reported nesting on cliffs and steep slopes, including Richardson's cackling goose (Branta hutchinsii), barnacle goose (Branta leucopsis), pink-footed goose (Anser brachyrhynchus), and Canada geese. Canada geese have also been reported to nest in trees and abandoned raptor nests (Lebeda & Ratti, 1983;Mackey et al., 1988;Nelson, 1953;Norment et al., 1999). Brief mention of Canada geese using elevated, manmade structures such as bridges, pilings, and city buildings can be found in Campbell et al. (1990), but with little detail. From a broader behavioral perspective, rooftops have been documented as resting locations for Canada geese in the autumns and winters (Dorak et al., 2017). Rooftops provide low predation pressures and warmer microclimates during these wintering months, which may explain Canada goose affinity to rooftops during this time (Dorak et al., 2017).
We report here the first detailed accounts of Canada geese using rooftops as nesting locations. Additionally, we describe nest materials, nest success, and clutch sizes of rooftop-nesting Canada geese in central Indiana. We suggest that this type of nesting behavior may provide additional challenges to managers and may produce additional nuisance behaviors associated with this species.

| OBS ERVATIONS
From March to July 2021, we monitored Canada goose nests in the Indianapolis Metropolitan Area (Indiana, USA). During our routine observations across three study areas, we found 5 nests on elevated rooftops. Nests were monitored on a weekly basis by capturing band information from the adults present as well as number of eggs observed. Fates for nests were assigned after hatching through observations of egg membranes and goslings present. defending an elevated nest. Note that the nest is composed of atypical materials of rock and a rubber automotive belt with little to no down/body feathers F I G U R E 3 Rooftop Canada goose (Branta canadensis) nest posthatch. Note the automotive belt that was used as a "liner" in Figure  2 was moved and instead a shallow depression in gravel was used as the nest for the second time in the 2021 season tance to nearest body of water (Table 1).
Canada geese that nested on rooftops produced fewer eggs that were more successful than geese that nested on the ground.
The number of eggs per nest varied, with a significantly lower mean clutch size in elevated nests (4.00 ± 0.71) relative to non-elevated nests (5.01 ± 1.37) in our study area (t = 2.82, df = 6.7, p = .0269).
However, there was no evidence of gosling mortality observed in any of the above-described nests. Goslings from nests 1 and 5 were rescued by researchers during routine nest checks of the field sites, indicating that rooftop nests may be potential traps for Canada goose goslings. Nevertheless, rooftop nests were 100% successful in hatching (Table 1), compared to 59.9% of nests found at ground level at our field sites (DJS unpublished data). While ground nests were typically made from plant material, feathers, and occasionally litter, rooftop nests were less likely to include feathers, and plant material, in general (Table 1).

| DISCUSS ION
With their growing populations, Canada geese in urban areas are increasingly viewed as a nuisance species due to their defecation, defensive behaviors, and property damage. While rooftop nesting has been documented in several avian species such as gulls (Soldatini et al., 2008), killdeer (Ankney & Hopkins, 1985), terns (Forys & Borboen-Abrams, 2006;Warraich et al., 2012), and nighthawks (Mays et al., 2019;Newberry & Swanson, 2018), such behavior in Canada geese has not yet been well-characterized.
This novel behavior could pose additional challenges in the form of new human-goose conflicts and could present additional need for management intervention. For example, rooftop nesting geese may be considered a nuisance to homeowners and property managers as they are defensive and territorial during the nesting period.
Interventions such as nest destructions or aiding goslings during nest departure, particularly if the rooftop has a barrier wall, will be necessary to mitigate human-goose conflicts.
We hypothesize that Canada geese may be selecting elevated nesting sites in urban areas to avoid predation and/or disturbance from ground predators, which would include typical mammalian predators (e.g., coyotes, foxes, and raccoons) and humans. This hypothesis is supported by data showing that elevated nests are more successful than ground nests in Canada geese (Krohn & Bizeau, 1980). Canada geese nesting on rooftops may have unsuccessful clutches from extreme heat, low gosling survival from nest departure, or lack of vital resources that are not found on roofs. Other studies indicate that structures and obstacles near the nest such as predator-proof fencing may pose a threat to brood survivability (Howerter et al., 1996;Trottier et al., 1994). Additionally, a number of studies suggest that extreme heat has a negative effect on egg viability in various avian species (Beissinger et al., 2005;Saino et al., 2004;Stoleson & Beissinger, 1999), though this did not appear to have any effect on the viability of Canada geese eggs in our study areas.
Our documentation here provides additional evidence to the myriad of ways wildlife species are interacting with novel human environments. Additional research is warranted to assess the frequency of elevated nesting across broader spatial scales and the fate of rooftop nests in metropolitan areas. Further understanding of this behavior could become quite useful to our future management of this important species.

ACK N OWLED G M ENTS
We thank A. T. Bird and B. D. Wehus-Tow for their assistance with field data collection. We are grateful to Ball State University, Franklin College, and the Indiana Department of Natural Resources for their support. Funding for the project was provided by Indiana Department of Natural Resources' Wildlife Restoration Grant W49R2.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no conflicts of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
All data are present in the publication.